I usually start off with a YT video or three. Simply because someone has done the same work and can give you tips to make it easier. Sometimes you need to start disassembling further away than is obvious. Like on 1997 Pathfinder the headlights are tiny but to remove them you have to remove the entire grill and bumper trim assembly first. Or with a timing belt on a Subaru; you can access the timing belt without removing the radiator but you'll probably damage it at the end unless you remove it. These are things that you don't want or need to learn the hard way.
Also, dedicated forums (think pre-FB PHPBB message boards) are excellent. They are not as popular as they used to be but the style is more conducive to problem solving conversing than Facebook groups. There are dedicated forums for most brands and models of vehicles and the people on there are usually experts. Like, "I own 7 of these cars, let me send you some parts" kind of experts. They genuinely want to participate in a community. Their car is their hobby.
Obviously Facebook groups and subreddits are out there for every topic but I find Reddit to be more for karma whoring and Facebook is more argumentative and punitive.
Most basic instruction manuals can be found on parts store websites like Auto Zone and Advanced Auto parts. They usually have basic schematics, walkthroughs, and exploded parts diagrams you need for reference. For example, when bleeding brakes you have to bleed the components in a specific order. A quick call to the parts store can provide you with the proper order, as each vehicle is different.
I also avoid buying car parts at non car part stores. Like Wal Mart. Also, cut open the box containing the new part AT THE PART STORE COUNTER before you leave. Countless times you get home and open a used part that someone stole out of the package and returned the old one to the store. It sucks buying new parts, getting home and they are actually used. Returning them in that state is always fun. It happens enough that you should really open the packages before leaving.
Alternators and starters, even if brand new should be tested on the tester at the parts store before leaving the store. My buddy bought 3 alternators for a Bronco just to install them and find the first two defective. We wasted a whole day on trips back and forth to the parts store.
Even better, starters and alternators can be brought to a rebuild shop instead. Usually you pay about the same as a replacement, but the rebuild shop does a nicer job and gives you a guarantee with a dyno print out proving the part works properly.